TR: The Danger Of Green Laser Pointers

[bystander]

The Danger Of Green Laser Pointers
Technology Review | the physics arXiv blog | 12 Aug 2010

Cheap green laser pointers can emit dangerous levels of infrared radiation, according to an investigation carried out by physicists in the US

Twenty years ago, a green laser would set you back $100,000 and occupy a good-sized dining room table. Today, you can buy a green laser pointer the size of a ball point pen for $15.

These devices create coherent green light in a three step process. A standard laser diode first generates near infrared light with a wavelength of 808nm. This is focused onto a neodymium crystal that converts the light into infrared with a wavelength of 1064nm. In the final step, the light passes into a frequency doubling crystal that emits green light at a wavelength of 532nm.

All this can easily be assembled into a cigar-sized package and powered by a couple of AAA batteries.

The result are devices generally advertised to have a power output of 10mW.

Today, Jemellie Galang and pals from the National Institute of Standards and Technology and the University of Maryland say they've found worrying evidence that the output of some green laser pointers is much higher and more insidious. They describe one $15 green laser pointer that actually emits ten times more infrared than green light.

Galang and co are under no illusion as to the potential consequences of this. "This is a serious hazard, since humans or animals may incur significant eye damage by exposure to invisible light before they become aware of it," they say.

And the problem appears to be widespread. "We have found that this problem is common in low-cost green laser pointers, though its seriousness varies widely," they say.

That's not a good state of affairs. Any ordinary user would be entirely unaware of the problem because infrared light is invisible. However, Galang and buddies describe a simple way for anybody to detect these infrared emissions.

The method is to reflect the the beam off a standard CD which acts as a diffraction grating, and so separates light of different wavelengths. The diffracted light is reflected onto a piece of paper which displays the diffraction pattern. Many webcams are sensitive to infrared light or can be easily modified to detect it. So photographing the paper using such a camera shows the diffraction pattern of the green light and any infrared light produced too.

The team hasten to emphasize the safety procedures that must be used during such an experiment.

They also take apart the green laser pointer in question to identify the cause of the problem. The design ought to include an infrared filter that blocks any infrared light that isn't converted to green light. However, the culprit they bought not only did not have the filter, it did not have a slot for such a filter. "We thus believe that the absence of the filter in this case was due to a design decision," they say

So somebody somewhere has removed the filter from the design, presumably to reduce costs. If that isn't a criminal act, it ought to be.

A Green Laser Pointer Hazard - J Galang et al

• arXiv.org > physics > arXiv:1008.1452 > 09 Aug 2010

[orin stepanek]

I don't own a laser pointer; we sold pointers in the pet dept. at Wal-mart for cats and dogs to chase. they were only 3 inches long and the thickness of a pencil. Kids used to take them off the shelf and play with them all the time. I can't recall if they were true lasers of not.
http://www.petco.com/product/108534/Las ... erralID=NA

[neufer]

http://www.colbertnation.com/the-colber ... er---bears

[Beyond]

So much for going green.

[Orca]

I was under the impression that laser light of any frequency shined in they eye could potentially cause damage.

Many of the green lasers available on the market can be as high as 500 mW or even 1 W (in contrast with the "cheap" ones, such as 5 mW red laser pointers). They do make handy tools for backyard astronomy; you can see the beam in the air and thus use them to point out constellations and such. 5 mW is plenty of power for this purpose (the visibility of the beam is due to its frequency - the light scattering in the atmosphere - not the intensity of the beam).

If laser pointers continue to gain popularity - and keep being abused - I would not be surprised if they became more heavily regulated. Just recently I heard a local news story about a police officer that was shot in the face with a green laser from a great distance; they weren't able to find out who did it. The officer suffered eye damage.

[bystander]

The danger here is the assumed low power of the laser. The lasers are advertised to be only 5 to 10 mW, and while the visible green light might well be in the advertised range, the leaked invisible infrared light was up to 10 times higher.

Here's another article from Wired Science, today: DIY Laser Safety: How to Test Pointers and Save Your Eyes.

[Orca]

Do most people look at the wattage on lasers?

True, the fact that the infrared emissions are far larger than the visible light and the devices are being sold without a filtering device is a bad thing. I just don't think anyone really thinks about the wattage.

But again, every laser device I've ever seen has a warning label. I would have thought by now just about everyone realizes that any laser light directed in the eye can cause damage (almost as obvious as the danger of looking directly at the sun).

But then again, people may think that a laser is a safe, fun toy because it's so cheap and readily available.

From the extra link you added:

The total power isn’t that much, about a thousandth of the output of a typical flashlight, Hagley noted. The danger is that laser light is a focused beam of a single wavelength of light, meaning 20 milliwats is enough to burn a hole in your retina before you blink.

[Chris Peterson]

From the extra link you added:

The total power isn’t that much, about a thousandth of the output of a typical flashlight, Hagley noted. The danger is that laser light is a focused beam of a single wavelength of light, meaning 20 milliwats is enough to burn a hole in your retina before you blink.

In fact, this is not true. A 20mw laser is just barely able to do some retinal damage, if you don't blink or avert, and if it's the right color. Permanent damage at this wattage with a visible light laser is rare. The risk is greater with IR, since you don't have a blink reflex to what you can't see. But in the case of green lasers, the IR component is highly uncollimated (unlike the green component), and is associated with a visible beam that does generate a blink reflex. So yes, such lasers could potentially cause permanent eye damage due to accidental exposure, but in reality the conditions required for this would be very unusual. There are much more dangerous things all around us that we should worry about before green laser pointers!